Peripheral NMDA and non-NMDA receptors contribute to nociception: An electrophysiological study

The present study investigated the effects of peripheral administration of N-methy-D-aspartate (NMDA) and non-NMDA receptor antagonists on C-fiber evo ked responses of the spinal dorsal horn neurons in the spinalized rats. Whe n DL-2-amino-5-phosphonovaleric acid (AP5) (10 mM, 1 mM, 0.1 mM, 20 mu l) o r 6,7-dinitroquinoxaline-2, 3-dione (DNQX) (1 mM, 0.1 mM, 0.01 mM, 20 mu l) was subcutaneously injected into the receptive field on the hindplantar re gion, C-fiber evoked responses of the dorsal horn neurons were profoundly i nhibited in a dose-dependent manner. Three hours after subcutaneous injecti on of carrageenan into the ipsilateral hindpaw, NMDA and non-NMDA antagonis t-induced inhibition of C-fiber evoked responses was more potent than that in the normal rat (Student's t-test, p < 0.05). In the carragenan-treated r ats, DNQX-induced inhibition was stronger than AP-5-induced one (Student's t-test, p < 0.05). The results suggest that peripheral NMDA and non-NMDA re ceptors are involved in mediating excitation of nociceptors. (C) 2000 Elsev ier Science Inc.